Monday, April 23, 2007

Christine Neil and Andrew Leigh have released a fascinating paper on the effects of the Federal Government’s gun buyback on murder and suicide rates in Australia. Generally the authors are careful to not read too much into their statistical findings but overall conclude that the buyback has reduced the number of murders from between 2–36 per year and the number of suicides from between 126-247 per year. This suggests significant overall effects of gun control on rates of suicide, in particular, but also possibly on the murder rate. This contrasts with the finding of no effect on murder rates and no explicable effects on the suicide rate in an earlier study by Baker and McPhedran here.

Neil and Leigh do not make strong claims in this regard – it is a hard call since homicide rates and suicide rates have been trending down strongly through time anyway. The punch line in the author’s claims is that homicide rates are bounded below at zero so that recent substantial decrements in this rate, since 1996, are very significant since the rate itself cannot fall below the natural barrier of zero.

In Andrew’s blogpost, though not in his article, he calculates the cost of the buyback at $500 million and then aggregates the suicides and deaths together to deduce that a minimum total of 128 lives per year were lost. Taking recent estimates of the value of a human life at $2.5 million he calculates that the buyback paid for itself in two years.

That sounds right if the value of a suicide prevented is taken at $2.5 million. But people presumably kill themselves when they feel their own lives are not worth living. Their incomes may be low, their prospects poor or they may suffer from serious debilitating diseases. In short to follow the ‘optimal suicide’ literature (Hamermesh and Soss) ‘as soon as the terrors of life reach the point at which they outweigh the terrors of death a man will put an end to his life’ (Shopenhauer, On Suicide). Adopting this viewpoint, preventing a suicide may not increase society’s wealth – it may in fact decrease it if you respect individual preferences. Presumably this is the idea behind the case for voluntary euthanasia.

Even if you dislike the macabre notion of attaching a zero welfare gain to preventing someone from killing themselves I am unsure that preventing people from killing themselves with a gun substantially reduces the suicide rate. Are not things like sleeping pills and carbon monoxide relatively painless substitute ways of killing yourself? If this is so then gun-driven suicides may be replaced with other types of suicides.

In either case, the cost-benefit case as presented becomes weaker. Including only the murders and maintaining a zero discount rate the results would suggest a net gain from the gun control measure if account is made of murders saved over 100 hundred rather than 2 years if the lower bound on effects is taken.

Another puzzling point that Neil and Leigh do not deal with is that suicide rates apparently declined for different forms of suicide - not just those involving guns. Thus the decline in the suicide rate might be hard to attribute to gun control.

Lest I be misunderstood I am in no way arguing that the ‘gun buyback’ was not good policy. This is only a qualification on what seems to me a very interesting study. I have lived in a society where there was widespread gun availability – Thailand – and I think that the fears that are a consequence of widespread gun ownership outweigh any benefits. The murder rate in rural Thailand while I lived there in the 1980s was massive and much of it was associated with gun use.

Actually, that issue about the impact of the buyback on the stock of guns poses an interesting question about its impact on gun suicides.

I think the buyback only applied to ceretain classes of weapons. I am guessing that these included fully automatic weapons and at least some semi-autoimatic weapons. I don't think it applied to bolt action rifles, some types of shotguns and some types of pistols. While it probably reduced the overall size of the gun stock in Australia, I suspect that it did so by less than the number of guns that were "bought back" by the Commoinwealth Government. The reason for this is that at least some of those shooters probably replaced the banned guns with alternative guns that were still legal. In addition to affecting the size of the gun stock, the gun buy-back probably also altered its composition.

I suspect that most (or at least many) gun related suicides do not involve the type of guns that were banned. As such, would we expect a large impact on gun-related suicides as a result of the gun buy-back?

And firearm suicides seemed to be falling off a bit pre-97 (partly due to higher than usual levels in the early 80s), while non-firearm suicides were increasing. Not much evidence that they were trending in the same direction before or after 1997 therefore.

But I somewhat despair: the graphs appear to be like Rorschach tests, with everyone seeing only what they want to see in them, which is why I rather prefer even flawed statistical analysis to all the story telling.

On the CBA: we did a back of the envelope because quite frankly half a billion sounds like a high cost, and we wanted to put it in perspective. And on the $2.5 million figure: your anecdotes apply nicely to the voluntary euthanasia case, but not too all suicides. I'll counter with my own anecdote: a friend of mine recently experienced a suicide in his family of a very intelligent, healthy and much loved young man. Putting the social benefit at zero in this case would be just wrong. It's probably much greater than $2.5m. But I don't think for a back of the envelope calculation, we can reasonably take that sort of heterogeneity into account.